DNA has a highly complex structure. In fact, it took numerous scientists along with countless experiments to figure out the accurate structure of DNA. Today I would like to share the structure of DNA that was deduced by scientists after a series of trials.
Complementary Base Pairing
The nitrogenous bases – a part of nucleotides – follow the complementary base pairing rules. Basically, in a double-stranded DNA, guanine (G) always pairs with cytosine (C), and adenine (A) always pairs with thymine (T). There are three hydrogen bonds between G and C, while there are 2 hydrogen bonds between A and T. Chargaff’s rule, which was founded by Erwin Chargaff, is related to complementary base pairing. Chargaff’s rule states that there should be equal amounts of guanine and cytosine and equal amounts of adenine and thymine.
Antiparallel Structure
In order for the complementary base pairing rule to be successful, the bases should be facing each other so that they can pair. Thus, the two strands run in opposite directions – in other words, antiparallel – to each other. Whereas one strand of DNA runs from 5′ to 3′, the opposite strand runs from 3′ to 5′. 3′ and 5′ refer to the exposed carbon on the sugars at the ends of DNA chains.
Using the rules above and additional information known about the chemistry of DNA, Watson and Crick built a 6-foot model out of a metal scrap that accurately reflects the structure of DNA. The key evidence they used to support their research was a photograph of a DNA X-ray diffraction taken by Rosalind Franklin and Maurice Wilkins. This model provided the first opportunity to visualize DNA and see how it fits into available evidence.
The story of Watson and Crick’s model leads us to an important discussion about models and investigation of the real world. Models and reality are somewhat contrary – a model is built on thoughts of scientists whereas the reality is based on concrete rules. As shown in the example of Watson and Crick, their initial models were inaccurate and flawed. However, as they overcame challenges, they were able to create a successful model for a double helix. Thus it can be concluded that although a model can be inaccurate at reflecting the reality, it can also be accepted by the scientific community and supported by further research when it is the product of countless trials and errors.
Works Cited
“History – Historic Figures: Watson and Crick (1928- ).” BBC, BBC, http://www.bbc.co.uk/history/historic_figures/watson_and_crick.shtml.
“How Is DNA Anti-Parallel? | Socratic.” Socratic.org, socratic.org/questions/how-is-dna-anti-parallel.
“Brent Cornell.” Lung Disorders | BioNinja, ib.bioninja.com.au/standard-level/topic-2-molecular-biology/26-structure-of-dna-and-rna/nitrogenous-bases.html.
The Science Herald 
Leave a comment